📘 Quick Concept
What is Solution Stability Testing, and Why Does it Matter?
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What Does it Check?
Solution stability testing asks a simple practical question: if a standard or sample solution sits in the autosampler tray or fridge for a while before it gets injected, does it still give the same result as when it was freshly prepared? If an analyst has to re-inject a solution the next day (queue delays, instrument downtime, large batches), this data tells the lab whether that re-injected result can still be trusted.
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How Does This Calculator Work?
The calculator is organized into five completely independent modes — Initial, 24 Hours, 48 Hours, 72 Hours, and Custom. You must pick one mode to begin — nothing calculates by default. Inside every time-point mode you then pick one of two independent boxes, Standard Solution Stability or Sample Solution Stability, each with its own complete data set. No mode or box ever borrows or mixes values from another — every calculation runs fresh, on its own data.
🧭 Quick Concept — Mandatory Mode Selection
Five Independent Modes — Nothing Calculates Until You Choose
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Initial
Your t = 0 baseline. Its own fresh Standard system suitability, its own formula constants, one sample reading. Gives the Initial Result % — the number every later Sample box measures itself against.
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24 Hours / 48 Hours / 72 Hours / Custom
Four separate time-point modes (Custom lets you type any duration). Each is a clean slate — selecting one never pulls in data from Initial or from any other time point.
Why no default mode? Silently defaulting to a mode risks an analyst calculating the wrong time point by mistake. Requiring an explicit click makes sure every calculation is the one you actually meant to run.
⚖️ Quick Concept — Two Independent Boxes per Time Point
Standard Solution Stability vs Sample Solution Stability
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Standard Solution Stability
Checks whether the working standard solution itself degrades in storage. Laid out exactly like the validated worksheet: this box has its own fresh standard system suitability, then the constants Weight of Standard, Dilution Factor of Standard, Concentration of Standard (calculated automatically = Weight × Dilution Factor) and a required Reference % (no default — you type whatever your SOP specifies). Dilution factors can be typed as an expression such as 1/50*5/100*10/50. Every fresh system suitability block shows Average, SD and %RSD. Then, for Room Temperature and Refrigerator separately: the sample Absorbance/Area and Weight of Spl (mg). The calculator gives Conc. Spiked (= Weight of Spl × Dilution Factor of Standard), Conc. Found (= Absorbance ÷ mean fresh standard × Concentration of Standard), Result % (= Found ÷ Spiked × 100) and %Difference against your Reference %. No dependency on Initial at all.
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Sample Solution Stability
Checks whether the actual tablet/sample solution degrades in storage. Laid out like the validated worksheet: this box has its own fresh standard system suitability, then the constants Weight of Standard, Dilution Factor, Average Weight, Label Claim, Potency of Standard and the Initial Result %. Then, for Room Temperature and Refrigerator separately: the sample Absorbance/Area and its own Weight of Spl (mg). The calculator gives mg/tablet, Result % and %Difference against the Initial Result %.
Where does "Initial Result %" come from inside a Sample box, if modes never share data? You type it in directly — exactly like a paper worksheet, where the Initial Result % is copied by hand into every later Sample block. If you already calculated Initial mode earlier in the same session, the calculator offers a one-click "Use This Value" button as a convenience — but the field stays a normal, editable input either way, and the Sample box's own calculation never silently reads Initial's live numbers.
Why does each box need its own fresh standard, instead of sharing one per time point? Keeping every box fully self-contained means you can fill in and calculate just the Standard side, just the Sample side, or both — in any order, on any device session — without one box's incomplete data blocking or skewing the other's result.
🌡️ Quick Concept
Room Temperature vs Refrigerator (2–8°C)
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Room Temperature (RT)
Represents the realistic worst case — a solution left on the autosampler tray or bench overnight without special storage. This is usually the condition most likely to show degradation first, if any occurs.
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Refrigerator (2–8°C)
Represents a controlled, cool storage condition. Comparing RT results against Refrigerator results across the same time points tells you whether refrigeration meaningfully extends how long a solution stays reliable — useful for deciding how solutions should actually be stored during a real analytical run.
🧮 Quick Concept — The Math
Result % and %Difference, Explained
Every number in this calculator boils down to two formulas, calculated fresh inside whichever mode/box is currently active.
| Term | What it Means |
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| mg/Tablet | The assayed strength, back-calculated from the peak area against that box's own fresh standard, corrected for weights, dilution, and potency. Calculated in Initial mode and inside every Sample box. |
| Result % | mg/Tablet expressed as a percentage of the Label Claim — the number you'd normally report for an Assay result. |
| %Difference | |Value A − Value B| ÷ [(Value A + Value B) ÷ 2] × 100 — a symmetric way of expressing how far two values are apart, relative to their average. Inside a Standard box, Value A is the Reference % you type into that box yourself — there is no default, so enter whatever your SOP specifies (commonly 100%). Inside a Sample box, Value A is the Initial Result % you entered in that box. Either way, Value B is that box's own freshly calculated Result %. |
| %RSD | Relative standard deviation of the fresh standard replicate readings entered inside that specific mode/box — confirms the instrument/column were performing correctly before you trust the readings at all. Every mode/box has its own independent set of replicates. |
Typical acceptance: %RSD ≤ 2.0% for system suitability, and %Difference ≤ 2.0% (tighter or looser per your method SOP) for both Standard and Sample stability, at both RT and Refrigerator. These limits are set once, globally, and applied to whichever mode/box you calculate — they are settings, not measured data, so sharing them doesn't mix any values between modes.
💡 Beginner Tip
Beginner Tips — How to Fill the Form
- Select Test & Instrument: Choose your test type (Assay, Dissolution, Content Uniformity, or Related Substances/Impurity) and instrument (HPLC or UV-Vis) at the top — this only relabels the page and the printed report ("Area" ↔ "Absorbance"); the underlying math is identical either way.
- Step 1 — Pick a Mode: Nothing else on the page unlocks until you click one of the five mode cards (Initial / 24 Hours / 48 Hours / 72 Hours / Custom). There is no default — this is deliberate, so you never calculate the wrong time point by accident.
- Start with Initial: Enter 5–6 replicate fresh standard readings (or as required by your SOP), the Formula Constants (Weight of Standard, Dilution Factor, Average Weight, Label Claim, Potency), and one sample reading (with its Weight of Spl, mg) at t = 0. Click Calculate — the Initial Result % shown becomes the reference you'll reuse later.
- Time-Point Modes — Pick Standard or Sample: Inside 24 Hours / 48 Hours / 72 Hours / Custom, choose ONE of the two big boxes. Each is entirely independent and needs its own complete data — picking Standard does not fill in, borrow from, or affect the Sample box, and vice versa.
- Standard box: Enter that box's own fresh standard replicates; then Weight of Standard, Dilution Factor of Standard and your Reference % (Concentration of Standard fills in by itself); then, for Room Temperature and Refrigerator, the sample Absorbance/Area and Weight of Spl (mg). Calculate — Conc. Spiked, Conc. Found, Result % and %Difference appear in the grey cells, exactly like the worksheet.
- Sample box: Enter that box's own fresh standard replicates; then Weight of Standard, Dilution Factor, Average Weight, Label Claim, Potency of Standard and the Initial Result % (type it in the last column, or click "Use This Value" if you already calculated Initial mode this session); then, for Room Temperature and Refrigerator, the sample Absorbance/Area and Weight of Spl (mg). Calculate — mg/tablet, Result % and %Difference appear in the grey cells.
- Custom mode: Also lets you type your own time-point label (e.g. "10 Days" or "6 Hours") before picking Standard or Sample.
- Switching modes/boxes: Use the "🔁 Change Mode" button to go back to the mode selector, or click the other box's card to switch — your entries in the mode/box you leave are kept exactly as you left them, ready to revisit, but are never combined with any other mode's or box's calculation.
- Acceptance Limits: Use your method SOP's specified limits for %RSD and %Difference — select "Custom Limit" if yours isn't in the dropdown. These apply globally to whichever mode/box you're calculating.
- Result: Each Calculate click reports Result % and %Difference for exactly the mode/box you're working in, at RT and Refrigerator where applicable — plus a Pass/Fail verdict, an SST band chart, an RT vs RF chart, and a full math log so every figure is traceable.
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